Blood clot filters are typically used in conjunction with thrombolytic agents and anti-coagulants to treat pulmonary embolism occurring within a patient. These devices are generally implanted within a vessel such as the inferior vena cava, and function by capturing blood clots (emboli) contained in the blood stream before they can reach the lungs and cause permanent damage to the body. To filter emboli, many conventional blood clot filters utilize a number of independent filter legs coupled to an apical head that can be expanded within the body to form a conical-shaped surface that collects the emboli without disturbing the flow of blood. Once collected, a natural clot lysing process occurs within the body to dissolve the emboli collected by the filter.
Delivery of the blood clot filter within the body is generally accomplished via an introducer sheath percutaneously inserted through the femoral (groin) or jugular (neck) veins. Such introducer sheaths are generally tubular in shape, and include an inner lumen configured to transport the filter in a collapsed position through the body. Once transported to a desired location within the body, the filter can then be removed from wall. A needle, hook, barb, prong, wedge or other attachment means disposed on the base of each filter leg can be used to secure the filter within the vessel.
The efficacy of the filter to capture blood clots is dependent in part on the ability of the filter to properly center when withdrawn from within the introducer sheath. Tilting of the filter may result if the apical head is not aligned centrally within the vessel, causing the filter legs to asymmetrically engage the vessel wall. In certain circumstances, tilting of the filter may affect the ability of the device to effectively capture emboli contained in the blood. To overcome this problem, more recent designs in the art have focused on filters having the ability to self-center when placed in the body. These designs, while providing a means to center the filter within the vessel, typically add to the complexity and size of the filter and accompanying introducer sheath.